A new study reveals rivers are emitting ancient carbon dioxide once thought safely locked away—reshaping our understanding of the carbon cycle and Earth’s climate defense system.
Key Points at a Glance
- Rivers emit CO₂ sourced from carbon stored for thousands to millions of years
- Over half of global river CO₂ emissions may be from these long-term stores
- This suggests Earth’s plants and soil are absorbing more CO₂ than previously estimated
- Study spans over 700 rivers across 26 countries and used radiocarbon dating
Rivers, long viewed as carbon conveyors for freshly decayed plant matter, are now under new scrutiny. Groundbreaking research led by the University of Bristol and published in Nature has revealed that rivers globally are releasing vast amounts of ancient carbon dioxide—carbon that’s been stored for centuries or even millennia in soil and rock.
This unexpected discovery changes the narrative of the global carbon cycle. Scientists previously assumed most river CO₂ came from young organic matter broken down within the last 70 years. But this study found that more than 60% of CO₂ released by rivers is much older—some dating back thousands of years, leached from deep soils or weathered rocks.
“The results took us by surprise,” said lead author Dr. Josh Dean. “We now see that old carbon stores are leaking out far more than we realized. This changes how we estimate Earth’s natural carbon balancing act.”
To reach this conclusion, researchers sampled over 700 river stretches in 26 countries, using radiocarbon dating to measure the age of carbon in CO₂ and methane emissions. By analyzing the amount of carbon-14—a radioactive isotope of carbon—they could determine whether the emissions were modern or ancient.
The implications are significant. Rivers emit around two gigatonnes of CO₂ annually, a sizable figure when compared to the 10–15 gigatonnes produced by human activity. The realization that half or more of river emissions come from stable carbon reservoirs means global models of carbon flux—and projections of climate change—need recalibration.
“This hidden release from what we thought were stable stores means the planet’s forests, plants, and shallow soils are likely working harder than expected to keep CO₂ levels in check,” noted co-author Dr. Gemma Coxon. That also suggests a greater role for nature-based solutions in climate mitigation.
What’s more, the team plans to investigate whether human activities like agriculture, deforestation, and climate-driven permafrost thaw might be accelerating this ancient carbon leak. If so, the natural feedback loops keeping CO₂ levels stable could weaken just as we need them most.
“This research helps us better understand how Earth breathes,” said Professor Bob Hilton of Oxford. “And it suggests we may have underestimated how much effort our ecosystems are putting into cleaning the air.”
Source: University of Bristol
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